1. Field of the Invention
This invention relates to radar systems, and more specifically to an improved antenna for use with short-range radar systems for locating reinforcing steel rods, pipes, and other nearby objects positioned behind or within a volume of, e.g., concrete, soil, or wood.
2. Description of Related Art
A requirement exists for a cost-effective system capable of precisely locating objects, such as reinforcing steel rods (rebar), pipes, and air bubbles, behind or within a volume of, for example, concrete, soil, or wood. Various devices and systems currently exist to locate these various objects, but all are either expensive or of limited capability.
To overcome disadvantages of other available systems, Zircon Corporation of Campbell, Calif., developed an improved radar system for locating, e.g., buried objects. This radar system is described in the U.S. Patent Application entitled "Swept Range Gate Radar System for Detection of Nearby Objects," which has been incorporated herein by reference.
The radar system described in that application transmits a pulse and senses a return echo. The radar system then provides indications of (1) the strength of the return echo, and (2) the time lapse between transmitting the pulse and receiving the return echo. The strength of the return echo provides an indication of the size and material of the object reflecting the signal, while the time lapse provides an indication of the distance (i.e., range) between the system and the object.
Such a radar system can make use of any of several conventional antennas, including monopole and pyramidal designs. One such antenna, a conventional two-sided pyramidal horn 10, is shown in FIG. 1. Horn 10 includes two conductive triangular plates 12A and 12B that diverge to form two sides of a pyramid. Triangular plates 12A and 12B are formed of a conductive material, such as aluminum, and are held in place with respect to one another by non-conductive members, for example, plexiglass rods 14A and 14B.
The monopole antenna described in the application entitled "Swept Range Gate Radar System for Detection of Nearby Objects" and the pyramid antenna 10 of FIG. 1 share several shortcomings. For example, when either one of these antennas is used to transmit energy into, or receive energy from, a solid volume of e.g. concrete, the impedance mismatch between the antenna and the volume of material results in potentially severe ringing and re-reflection of the pulse energy at the antenna/concrete boundary. This ringing, or "first surface effect," wastes power and limits the minimum usable range of antenna 10 because the ringing masks return echoes that occur within the ringing period. Therefore, an improved antenna that decreases the first surface effect is needed.